1. Field of the Invention
The invention relates to a gas cooled high temperature reactor charged with spherical fuel elements, housed in a prestressed concrete pressure vessel having a cavity clad with a liner. A reflector surrounds the pile of fuel elements on all sides, and a hot gas collector chamber is located under the bottom part (bottom reflector) of the reflector. The hot gas collector chamber is bounded in the downward direction by the graphite blocks of the bottom layers of the high temperature reactor. A thermal bottom shield and a core support space is located between the thermal bottom shield and the bottom liner of the cavity, together with means to add and to remove the spherical fuel elements. The means to remove fuel elements comprises at least one ceramic pebble outlet tube passing through the bottom reflector and the bottom layers and one metal pebble outlet tube located under the bottom layers.
2. Description of the Prior Art
High temperature reactors are known from West German Offenlegungsschrift No. 30 30 510. Spherical fuel elements may be added to and removed from the core continuously after their depletion. The nuclear reactor has very high gas temperatures in its lower part. The bottom reflector, the bottom layers, and the part of the pebble outlet apparatus located within the core structure are constructed of highly heat resistant material. These structural parts are made of a ceramic material, such as graphite, which has a limited degree of tensile and bending strength. The part of the pebble outlet apparatus located outside the thermal bottom shield, which connects the ceramic outlet tubes with an isolator and subsequent scrap separator each, is made of metal to increase its mechanical strength. Preferably, an austenitic material is used, as there is a high neutron flux in the area concerned.
The state of the art is represented by an outlet tube for spherical fuel elements described in West German Offenlegungsschrift No. 31 21 379. The outlet tube is conducted through the bottom of the prestressed concrete pressure vessel in a passage lined with an armored tube. In order to make possible accurate installation of the outlet tube in the armored tube and subsequent levelling, the outlet tube is fastened to the armored tube at its upper end by means of a special suspension which extends above the bottom of the pressure vessel. This suspension further allows for compensation of the different thermal expansions of the outlet tube and the armored tube.
West German Offenlegungsschrift No. 24 49 430 is further cited as representing the state of the art, it also concerns the compensation of the thermal movements of two interconnected structural parts. These two structural parts are partial segments of a pipeline exposed to high pressure and high temperatures, joined together by means of a sliding joint operating on the principle of piston rings.